Specific Heat

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Objective

Students will be able to explain the concept of heat capacity and how to figure out the amount of energy transferred between substances through taking notes, performing practice questions, and participating in demonstrations.

Big Idea

Heat capacity is the amount of energy required to raise the temperature of a substance and can be determined through experiments and calculations.

Introduction

In this lesson students are introduced to the concept of specific heat.  This is done through notes, demonstrations, and practice questions.

  • This lesson aligns with the Next Generation Performance Expectation of  HS-PS 3-1 Create a computation model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.  It does so because students are learning how specific heat relates to energy flow as well as how to calculate the amount of energy absorbed or released using the specific heat equation.
  • This lesson aligns with the Next Generation Crosscutting Concept 5: Energy and matter.  It does so because students are thinking about specific heat and how energy is transferred between systems.
  • This lesson aligns with the NGSS Science and Engineering Practice 6: Constructing Explanations: It does so because students are expected to explain why various phenomena that occur within the demonstrations they observe.

For this lesson various resources are needed for the demonstrations including:

  • one 2-liter soda bottle per class
  • a blow torch
  • ring stand and 2 iron rings
  • bag of flaming hot cheetos
  • 3 metal paper clips
  • one soda can per class (or per few classes is okay)
  • 250mL graduated cylinder
  • matches
  • ring stand with two iron rings
  • ceramic triangle
  • ceramic crucible
  • clay
  • temperature probe (or thermometer)

Engage

30 minutes

To engage students in this lesson I have them perform two different review activities.

  1. I first have students do Frayer models for the terms exothermic and endothermic.
    • I do this by passing out the frayer models paper with the terms exothermic and endothermic.
    • I then instruct students to use their notes to fill in the applicable information for the two terms
    • This activity takes students about 10 minutes.  As students are completing their models I have them share with their table groups.
    • When most students are done and have shared with their partners I choose a couple of students to share what they came up with.  As they share their models I put their individual paper on the document camera so all students in the class can see the example.
    • Here is one student example.
    • Frayer models is a great strategy to help students dissect these complicated words.  For more details on Frayer models see my Frayer model reflection.
  2. I then have students do quick practice on exothermic and endothermic reactions.
    • This is similar to how I have students do whiteboards (see Unit 1 lesson on significant figures for details on Whiteboard Practice).
    • I use this PowerPoint.
    • I show students the first slide of the powerpoint and tell them how they are all going to work on their own and simply hold up the symbol x for exothermic and the symbol d for endothermic.  As I explain this I show them how to make the symbols with their fingers. 
    • I then put up the examples one by one and wait for students to show their answers. As I do this I give students the correct answers.
    • This activity takes about 15 minutes.
    • I really like this strategy because it gives students a chance to check their understanding of exothermic and endothermic reactions (which many get confused) in a simple and effective manner.

Explore

10 minutes

To begin the new material for the lesson I have students begin to explore what they already know about specific heat. 

I do this by showing students the first slide of the PowerPoint which has a picture of a playground and the question, "It is a warm day and you go to the park.  Is everything going to feel the same?  Why/Why not?"

I tell students to take about 3 minutes to try to answer the question on their own by jotting down a few ideas at the top of their notes organizer.

As they are getting done with this I tell them to turn to one of the partners at their table and discuss the question.  I tell them that if there partner has some insight that they can feel free to change their answers that they wrote down.

After giving student a few minutes to talk with their partners I call on a few groups to share out their ideas.

Some of the examples of what students say include, "the metal parts feel hotter", and "the slide is really hot".

This is an example of one student's responses on the top of their Graphic Organizer.

 

Explain Part I

10 minutes

For this section of the lesson I introduce the concept of specific heat and the idea that it plays are role in how quickly substance "heat up". 

  • As I teach this to students I make sure to talk about what it means to resist changes in temperature as "the temperature does not change very quickly" and "it takes a lot of energy to make the temperature of the substance change"

Elaborate Part I

15 minutes

In this section of the lesson I elaborate on the idea of heat capacity through performing a demonstration for students.  The demonstration is on the 5th slide of the PowerPoint and at the bottom of the first page of their graphic notes organizer.

  • I begin by asking for two student volunteers.  I choose two students from hands that go up and let them know I will use them soon.
  • Next I show students the top of slide 5 of the PowerPoint.
  • I then show students my setup of a 2-Liter bottle filled with water attached to a ring stand between two iron rings I then ask them the first question of the demonstration, " What do you expect to happen to the water filled soda bottle when a blow torch is used on it?"  I show students how I will light the blow torch and then hold it pointed to the soda bottle.  I give students 2 minutes to record their predictions.  I then tell students, "make sure that your partner has something written down and if not give them a nudge and tell them to get writing."  I give students 1 more minute and then let them know that we are going to move on.
  • I ask the first volunteer to come up, have him or her put on goggles, and show them how to use the blow torch.  I then help them to light the blowtorch and point it at the soda bottle.  I make sure that they move it around a bit as they point it to the bottle.  I have them hold it there for about 30 seconds in which time there may spring a small leak with water squirting out, but the bottle usually holds up just fine.
  • I then show students the next question, "What happened?" and have them write something down.  As they are writing I take the cap off of the bottle and have the volunteer feel the water.  I have him or her report to the students what if feels like (its warm) and then proceed to pass the bottle around for students to feel.  I then thank the volunteer and have him or her take their seat. 
  • Next I pose question #3 to the students, " What do you expect to happen when the water is taken out of the bottle and the blowtorch is used?"  I explain to students how I will pour the water out and then try the experiment again.  I give students 2 minutes to record their predictions.  I then tell students, "make sure that your partner has something written down and if not give them a nudge and tell them to get writing."  I give students 1 more minute and then let them know that we are going to move on.n
  • I ask for the second volunteer to come up, have them put on goggles, and show them how to use the blowtorch.  I then help him or her to light the blowtorch and point it at the soda bottle.  I only have him or her point it for several seconds because it quickly starts to burn the bottle.
  • I then thank the volunteer and pose the 4th question to students, "Explain the different results using the term specific heat".  I give students 5 minutes to record their answers.  I tell students to look back at their notes and to work with their partners if they are not sure of the answer. 
  • After about 5 minutes I ask if any students are confident in their answers, or their partners answers, and want to share out.  I call on a few students to share.  I explain to students that, "the water has a higher heat capacity so it is able to absorb energy from the blow torch; therefore, helping to protect the plastic that has a low heat capacity.  I explain to students that when the water was removed it no longer was there to absorb the energy of the blowtorch so the plastic burned". 
  • This is an example of one students filled in notes with answers to the demonstration.

Explain Part II

15 minutes

In this section of the lesson I teach students the equation q=mcDT on slides 6-8 of the PowerPoint and the top of the second page of the notes graphic organizer.  

  • On slide 6 I give students the equation and go over what each of the symbols mean.
  • On slides 7 and 8 I go over 2 examples with students.  I make sure to show students how we underline what we know, circle what we want, find the equation to use and then plug and chug with the equation.
  • Here is an example of one student's filled in notes with the answers to the example questions.

Elaborate Part II

15 minutes

To help students better understand how to use the specific heat equation and its purpose I do another demonstration of how to figure out the amount of Calories in a burning hot Cheeto.

I first have 3 students perform the lab for the entire class.

  • I begin by asking for 3 volunteers.  I pick students based on hands that go up and then let them know I will call them up shortly. 
  • I then pose the question to students, "How do we figure out the amount of Calories in our food".  I expect students to answer that we look at the nutrition label on the packaging.  I then ask them how companies like Frito Lay determine this and explain that we can use a calorimeter to determine this.
  • I then show students slide 9 of the PowerPoint and instruct them that they will be filling in information at the bottom of the 2nd page of their graphic notes organizer
  • Next, I call on the volunteers to come up and tell them that they are going to be doing the lab for the class.
  • I have student #1 pick out a Cheeto from a bag of Flaming Hot Cheetos and have them skewer it onto the burning device (a crucible with clay in the bottom and a paper clip- this is a picture of it)
  • I have student #2 be in charge of measuring 200.0mL of water with a graduated cylinder, pouring it into a soda can, and then hanging the can of water off of one of the iron rings and sticking the temperature probe inside of it (this is a picture of it).
  • I have student #3 be in charge of finding the initial mass of the Cheeto/crucible and give him or her the matches.
  • I have student #3 share out the initial mass and I record on one of the graphic notes organizers under the document camera and have the class copy onto their individual papers.
  • I then have student #2 report the initial temperature of the water to the class and both the class and I record on the graphic organizer.  I then have the student press collect on the computer to begin recording the temperature.  I choose to use a temperature probe in this experiment to help make finding the maximum temperature easier.  For more details on using probes in the classroom look at my Probeware reflection in the Elaborate Section of my lesson on temperature.
  • I have student #3 place the Cheeto/burning apparatus on a ceramic triangle/iron ring under the can/water/thermometer so that its very close (this is a picture of the setup).   I then have him or her light the match to make the Cheeto burn.  The Cheeto burns very quickly.
  • As the Cheeto burns I have student #1 check out the temperature and let us know the maximum that the water reaches.  The class and I record this on the notes graphic organizer.
  • When the Cheeto is done burning and the maximum temperature has been reached I have student #3 reweigh the burnt Cheeto on the apparatus and the class and I record this on the notes graphic organizer.
  • I then thank the 3 volunteers and have them return to their seats. 

I then lead the students through the analysis questions.

  • For the first question they determine the amount of calories using the heat capacity equation.  I make sure remind them that we need to use the grams of water and that the density of water is 1 g/ml so 200mL = 200g.
  • For the Second question students divide their answer in question #1 from the mass of Cheeto burned (I remind them to subtract the mass final mass of the Cheeto/crucible from the initial mass of the Cheeto/crucible).
  • For the third question I remind them that we have been doing calculations in calories but for food Calories we need to divide by 1000.
  • For the fourth question I pass the Cheetos bag to one of the students and have them figure out the Calories per gram using the nutritional information grams and Calories per serving.
  • For the fifth question students calculate the % error (which is always VERY high).
  • Finally for the sixth question students reflect on why its such a high % error.  The best response which I lead student to is that heat does not go directly from the Cheeto to the water in the can and that a lot of heat goes to the surrounding air.  Some other errors include weighing/measuring, energy absorbed by the can, and not capturing the highest temperature of the water.  Some students want to say that the size of the Cheeto is an error but I remind them that we account for this by finding the actual mass burned.

This is an example of one student's filled in graphic organizer with answers to the Cheeto Lab demonstration.

Evaluate

To evaluate student learning I have them perform homework related to heat capacity. 

  • The homework is found on the last page of their graphic notes organizer.
  • Students complete the homework at home and I check for completion the following day by giving a stamp.
  • I then go over the answers to the homework using the answer key.
  • This is an example of one student's completed homework. 
  • Some of the common mistakes of students include:
    •  knowing that the substance with the lowest heat capacity will heat up the fastest (#1)
    • correctly explaining the difference in heat when a city is on the water with the water absorbing some of the energy so not as hot.
    • correctly plugging into the equation to calculate energy.